Soil mineral nitrogen and the rating of CaCl2 extractable nutrients

Abstract

It was assumed that the determination of the mineral nitrogen (Nmin) content in the 0.01 mol/L CaCl2 could rely on measurements of single form NO3–-N, NH4+-N or both, and even including other extractable nutrients. This hypothesis was verified based on some primary data from 17 fields: ten with oilseed rape and seven with maize as indicatory crops during three consecutive seasons in a production farm in Górzno, Poland. The contents of NO3–-N, NH4+-N, P, K, Mg and pH were measured in soil prior to the spring vegetation start and after a crop harvest (autumn). Phosphorus in spring and NH4+-N in autumn, were variables discriminating against the number of clusters. It was higher in cropping sequences (CSs) with maize than with oilseed rape. The reliability of Nmin determination and distribution between clusters in spring based only on NO3–-N was fully corroborated for maize CSs. In autumn, irrespective of the CS, the decisive factor in Nmin prediction and distribution over clusters was the NH4+-N pool. This study resulted in the rating of CaCl2 extractable nutrients, indicating their availability status, shortage or excess, on the background of the Nmin temporary rating.